1. Field of the Invention
The disclosure is directed to a hydraulic controller arrangement for the pressure medium supply of a hydraulic consumer whereby a load having a high mass may be moved.
2. Description of the Related Art
Hydraulic controller arrangements consist of a pump that adjusts depending upon the highest load pressure of the respective actuated hydraulic consumers such that the pump pressure exceeds the highest load pressure by a predetermined pressure difference. These are also referred to as LS (“Load-Sensing”) systems. DE 199 04 616 A1 describes the basic principle of such LS controls.
Specifically, LS controls are used in situations where large masses are to be moved in a horizontal plane by means of the hydraulic consumers. An example of this is when the rotating gear drive mechanism of a mobile equipment and high pressures manifest during acceleration owing to the inertia of mass, which are, however, quickly reduced as soon as the mass has been set in motion. This can occur when the rotating gear has reached its desired rotational speed. It may result in a short-term advance of the mass, for example when the friction of the mass on the ground on which it is moving is very low. This advance of the mass is accompanied by an unintended modification of velocity. In hydraulic drive mechanisms including a controlled delivery quantity (LS control), this results in a pressure drop in the delivery line and in a deceleration of the mass, so that the latter has to be accelerated again in order to attain the desired velocity. Accordingly, the movement of the mass is subject to oscillations owing to the repeatedly occurring acceleration pressures.
It is known that by means of a return-side throttling of the pressure medium flow rate a back pressure may be generated which prevents an advance of the mass and thus provides for the desired stability of control. This throttling is customarily achieved when a drain control groove adapted to the supply control groove generates a backup pressure which may have various levels depending on the pressure medium flow rate.
It is a problem that at a very small pressure medium flow rate, a harmonization of the drain cross-section with the supply cross-section is very difficult to achieve due to the very small opening cross-sections, so that the oscillations mentioned at the outset may again occur at low velocities.
In contrast, the invention is based on the object of furnishing a hydraulic controller arrangement whereby a control of consumers without oscillations is possible even at low pressure medium flow rates.
This object is achieved through a hydraulic controller arrangement having features including a pressure medium supply of a hydraulic consumer whereby a load having a high mass may be moved.
In accordance with the invention, in the drain of a hydraulic consumer a drain backup valve is arranged whereby a drain branch line leading to the tank may be controlled open before or during the opening of the drain cross-section. For example, in a first stroke range of a regulator of a directional control valve of the hydraulic controller arrangement the returning pressure medium is conducted not via a drain control groove of the regulator but via the cross-section opened by the drain backup valve which assumes the function of throttling the return quantity. The drain backup valve may very easily be adapted to the low pressure medium flow rates, so that it is possible to control consumers at low velocities without the occurrence of oscillations.
In a particularly preferred variant, a shut-off means or the like is provided downstream or upstream of the drain backup valve, whereby the drain branch line may be shut off during a predetermined stroke of the regulator of the directional control valve. Thus it is ensured that, e.g., in the closed position of the regulator or during an initial stroke, the drain backup valve may open the drain cross-section, so that control of the consumer is achieved solely through the intermediary of the cross-sections that are opened or closed, respectively, by the regulator.
In a particularly compact embodiment, these shut-off means for shutting off the drain branch line means are integrated into the directional control valve and formed by a control edge of the regulator of this directional control valve.
The construction of the control arrangement may be simplified further if the backup valve and the drain branch line are also integrated into the directional control valve, preferably in the regulator thereof.
In an embodiment having a particularly simple construction, the drain backup valve is formed by a closing body biased against a valve seat by a spring, such as a sphere.
In the known solutions, the load pressure is tapped at the associated consumer through the intermediary of a load reporting passage extending through an end portion of the regulator. In such constructions it is advantageous if this load reporting passage and a part of the drain branch line extending in the regulator are arranged in the regulator in parallel and laterally staggered relative to the valve axis.
As an alternative for this solution, it is also possible to insert a sleeve in the regulator, in the axis of which the drain branch line extends, while the load reporting passage is formed by one or several longitudinal grooves provided at the outer periphery of the sleeve.
In the case of double-action consumers, a drain backup valve may be associated to each work port of the directional control valve.
Further advantageous developments of the invention are subject matter of further subclaims.